• Two simultaneous lines of research in development of garnet scintillators have been developed in the project. ISMA has optimized composition and crystal growth conditions by the Czochralski method of YAG:Ce crystals codoped with divalent codopants, while ILM group developed GAGG:Ce-based scintillators with the same dopants growth by the micro-pulling-down method. Both crystals were optimized by the feedback from CERN.
• The obtained results certify that scintillation parameters of Ce-doped YAG and GAGG are improved at certain combination of Ca and Mg codopants, which eliminates carrier traps and accelerates carrier transport to luminescence centres independently on the host composition.
• Apart of that, YAG is more promising as host, because it can be obtained in cheap W/Mo crucibles in contrast to GAGG and other Ga-containing crystals. Moreover, it does not contain Gd ions, which may call slow components in scintillation decay due to energy transport via Gd3+ sublattice. Moreover, Gd is a heavy atom, which may be subjected to radiation damage by charged hadrons in high energy physics experiments.
• Due to the synergy between Ca2+ and Mg2+ doping of garnets hosts, we demonstrated that improved combination of light yield and decay time can be achieved in Ce-doped garnets, i.e. larger number of prompt photons can be generated for fast-timing applications.
• Addition of dopants (Ta, Gd, Al) has not improved scintillation parameters but worsened crystallization conditions, resulting in larger quantity of inclusions in BSO/BGSO crystals.
• Transfer to BGSO solid solutions, although provided congruent melting and growth by the Czochralski method, did not enhance crystal quality because of cracks generated by SiO2 inclusions called by bismuth dioxide evaporation, and large difference in ionic radii between substitutional Si4+/Ge4+ cations creating mechanical stress in crystals.
• Coincidence timing resolution (CTR) of undoped BSO was improved to 125 ps by tuning growth atmosphere composition that provides minimization of SiO2 evaporation and reducing amount of Pt dissolving into the melt and, consequently, decreases the number of inclusions in crystals. As BSO is crystallized from Bi2O3-enriched melt-solution, further optimization of growth conditions is necessary to get large-size crystals with acceptable optical quality and enhanced radiation hardness.
• The decay time of GAGG:Ce,Mg fiber-shaped crystals decreased with Mg content to 0.5-2 ns, whereas light yield was below 2000 ph/MeV; the parameters were stable along the fibers grown by the micro-pulling-down method. Further tuning of Mg and Ca dopant content is necessary to determine optimal composition to grow large GAGG-based crystals by the Czochralski method.
• In the framework of R&D for the upgrade of the electromagnetic calorimeter of LHCb upgrade a cojoined work between CERN EPR&D and PICOcal group from LHCb collaboration development of W absorber made by 3D printing has been pursued. First prototype consisting of three blocks of 121.2x121.2x50 mm3 have been produced with 8x8x81 holes of 1.2x1.2mm2 for insertion of crystal fibres.
